Certain vehicles are powered in an electric vehicle (EV) mode using one or more traction motors. Each motor is energized by a high-voltage energy storage system (ESS), which may be recharged during vehicle operation or by using an offboard power supply. Hybrid electric vehicles (HEV) in particular can selectively use an internal combustion engine as a power source either alone or in conjunction with the traction motors. Typically, an HEV can operate in an EV mode up to a threshold speed before transitioning to at least partial use of engine power.
A transmission is used to transfer engine and motor torque to a transmission output member via one or more clutches. The output member ultimately powers drive wheels to propel the vehicle. A state observer may be used aboard the vehicle to provide state estimations of various required control parameters. A proportional-integral (PI) control module can provide feedback control over an oncoming or offgoing clutch, or any other rotating member of the powertrain.